Effects of sublethal doses of imidacloprid on the fecundity of green leafhoppers, Nephotettix spp. (Hemiptera : Cicadellidae) and their natural enemies

Laboratory and field experiments were conducted to examine whether a sublet hal dosage application of imidacloprid can induce physiological or ecologic al resurgence in the green leafhoppers Nephotettix virescens and Nephotetti x cincticeps. Fecundity of N. virescens and N. cincticeps exposed to imidac loprid-treated rice seedlings was reduced to one-third and one-half, respec tively, that of insects not exposed. Effect of imidacloprid on egg parasito ids of N. virescens was not detected because the percentage parasitism of N . virescens eggs was very low. The number of N. virescens adults consumed b y a lycosid spider Pardosa pseudoannulata which was exposed to imidacloprid -treated rice seedlings for the last 24h before experiment was significantl y lower than that on untreated ones. However, the number consumed by a spid er fed prey treated directly with imidacloprid was not significantly differ ent from that of untreated prey. Survivorship of the mirid bug Cyrtorhinus lividipennis and the proportions of AT. cincticeps eggs preyed on by bugs e xposed to imidacloprid-treated seedlings or fed on eggs laid in the stems o f treated seedlings were significantly lower than those of untreated ones. The results suggest that a sublethal dosage application of imidacloprid doe s not cause physiological resurgence in both green leafhopper species but i t does induce ecological resurgence.